Thursday, January 18, 2018

How To Create Or Increase Swap Space In Linux

The operating system makes use of swap space when its available physical
memory (RAM) is running out due to ever demanding applications. In this
situation, the operating system moves the inactive pages in physical
memory to swap space.

This freeing up of physical memory
will be used for other applications. When the physical memory is
available enough, the swap memory area will be brought back to the
physical memory. The administrators ensure that sufficient swap space
present in the system so that some free physical memory always available
to the operating system.

This article provides steps to create or increase swap space and also delete if you need.

​Do I really need swap space?

Not always, provided system has a large amount of physical memory (RAM).
But it is recommended to have swap space handy. The system may crash
when the system is run out of physical memory when many applications are
running with large memory foot print. When compared to RAM, disk space
is relatively cheap!

Partition or file?

Swap space can be a dedicated swap partition (recommended), a swap file,
or a combination of both. By default, most of the Linux distributions
create a dedicated swap partition or a file on the system partition
during installation. Windows operating system generally has the swap
space as a file.

What is the recommended swap size?

Though there is no hard and fast rule to have swap space, it is
recommended to have at least 1.5 times of the physical memory. In case
of hibernation, the swap partition should be at least as big as the RAM size.

Creating swap space

Following are the instructions to create swap space using a file:
​

Login as root.

Create swap file in directory “/var” with name “swapfile”. At the shell, create the file and set root permissions as follows:

Use “dd” command to fill the swap file with 1 GB size (as an example) as follows :

Now setup the swap file:

Enable the swap file:

To check whether the new swap file was successfully created, either of the below commands can be used.​

# cat /proc/swaps
# swapon –show

Add below line to the “/etc/fstab” file so that next time when the system boots, it enables the newly created swap file:

/var/swapfile none swap sw 0 0

Disable and remove a swap file

Disable the swap file.

# swapoff /var/swapfile

Delete the swap file.

# rm /var/swapfile

Remove the entry from “/etc/fstab” file.

/var/swapfile none swap sw 0 0

Limitation

Swapping mechanism does have a downside. Because the swap space resides
in hard disks, the access time for swap is slower and hence it cannot
be a complete replacement for the physical memory.

​Conclusion

System administrators can benefit greatly by adding sufficient swap
space to keep the system running smoothly. Regular monitoring of system
memory usage helps in determining the size of the swap space.